The invention relates to an X-ray device for the formation of slice images of an object to be examined which includes an X-ray source, an X-ray detector, a transport device for moving the object to be examined during the acquisition of a series of X-ray projection images of the object to be examined in a movement plane situated parallel to the imaging plane, and a control device for controlling the acquisition of the X-ray projection images and the transport device. Slice images of the object to be examined are formed from the X-ray projection images by a tomosynthesis method.
The invention also relates to a corresponding method for forming slice images of an object to be examined.
The formation of slice images by tomosynthesis is known in the art. The X-ray source and the X-ray detector are moved in opposite directions in parallel planes for the acquisition of X-ray projection images of an object to be examined that is arranged between the planes. This movement is performed such that a projection line between the X-ray source and the X-ray detector, that is, the connecting line between a focal point of the X-ray source and the center of the X-ray detector, extends through the same point of the object to be examined for each X-ray projection image. Different slice images can then be formed by simple addition of the image values that are associated with a voxel of a slice to be imaged of the object to be examined in different X-ray projection images. The object to be examined itself is not moved during the acquisition of the X-ray projection images.
German Patent Publication No. DE 197 56 697 A1 describes a device for X-ray tomosynthesis of parcels. A parcel is moved linearly through an X-ray system by means of a transport device. The X-ray system includes at least three X-ray scanning units whose fan beams are configured such that the parcel is simultaneously irradiated at different angles.
According to the known method, in all cases only the examination of a very limited part of the object to be examined is possible. For the examination and the formation of slice images of large objects, the method must be carried out several times in different regions of the object to be examined, after which the separately formed slice images can be combined, if desired. However, it is desirable to enable the inspection of large areas of the object to be examined merely by way of a single execution of the method and to form slice images of a large area within the shortest possible period of time, for example, the formation of whole body slice images of a patient or slice images of large pieces of luggage in the case of a luggage inspection application.
Therefore, it is an object of the invention to provide an improved X-ray device and a method in which slice images of large examination zones can be formed within a short period of time.
This object is achieved in a device and method in accordance with the invention by arranging the X-ray source and the X-ray detector to be static, i.e., stationary, during the acquisition of the X-ray projection images and configuring the control device such that the speed of the motion of the object to be examined and the instants or moments of acquisition of the X-ray projection images are selected such that all points to be imaged in an examination zone of the object to be examined are imaged in at least 10, but preferably in at least 50, different X-ray projection images.
The invention is based on the recognition of the fact that it is advantageous to move the object to be examined, that is, the patient or the piece of luggage to be inspected, instead of the X-ray source and the X-ray detector during the acquisition of the X-ray projection images. The moments of acquisition of the X-ray projection images and the speed of movement of the object to be examined are then optimized for the relevant tomosynthesis method, preferably being of the digital type in the present case, such that each point of the examination zone to be imaged in the object to be examined appears in at least a minimum number of X-ray projection images, this minimum number amounting to at least 10, but preferably to at least 50 or even from 100 to 200, so as to achieve an adequate image quality. This number, however, is dependent to a high degree on the type, on the condition and on the size of the object to be examined. This makes it possible to form slice images of large objects after a single execution of the method in accordance with the invention, for example, whole body slice images of a patient as they are necessary for trauma scanning. Moreover, the X-ray device and the method in accordance with the invention can be used for the testing of materials and for the inspection of luggage; integration in an existing processing chain is then also possible.
In order to optimize the tomosynthesis angle, that is, the angle of aperture of the X-ray beam that emanates from the X-ray source so as to traverse the object to be examined and be incident on the X-ray detector, the distance between the X-ray source and the X-ray detector can be varied in one embodiment in accordance with the invention. It is also possible to adapt the position of the X-ray source in a direction that is perpendicular to the detector plane, corresponding to the imaging plane, while the X-ray detector is arranged so as to be stationary. Consequently, the tomosynthesis angle can be optimized such that the image quality is optimized. The larger the tomosynthesis angle, the better the image quality will be. The position of the X-ray source, however, preferably is not changed during the acquisition of the X-ray projection images.
In a further preferred embodiment of the invention, at least two series of X-ray projection images are acquired while the X-ray source occupies a different position each time. Preferably, the X-ray source is then asymmetrically arranged relative to the detector, that is, for example, such that it faces the left edge zone of the detector during the acquisition of the first series and the right edge zone of the detector during the acquisition of the second series. This embodiment enables a further optimization of the tomosynthesis angle and hence the image quality.
The tomosynthesis angle can be optimized even further by means of at least one further X-ray detector that is included in a further embodiment of the invention and is arranged adjacent the first X-ray detector.
Preferably, in accordance with the invention, the transport device is moved at an irregular speed and in different, changing directions for the acquisition of the X-ray projection images. It has been found that the formation of artefacts in the slice images can be reduced or even avoided when the object to be examined is not rectilinearly and continuously moved at the same speed through the X-ray beam during the acquisition of the X-ray projection images, but is moved in a kind of xe2x80x9cchaoticxe2x80x9d way while the speed and the direction of movement change continuously. It may even be advantageous to move the transport device manually and completely irregularly, because the fewest imaging defects and artefacts then occur.
Further advantageous embodiments are disclosed below. It is to be noted that the method for the formation of slice images in accordance with the invention may be elaborated in an identical or similar way as the X-ray device described above and may be realized in versions as described above for the X-ray device in accordance with the invention and as disclosed below.